The present invention relates to a novel orally administrable controlled release unit dose formulation for the administration of pharmaceuticals. In the prior art many techniques have been used to provide controlled and extended release pharmaceutical dosage forms in order to maintain therapeutic serum levels of medicaments and to minimize the effects of missed doses of drugs caused by a lack of patient compliance.
Certain prior art extended release tablets containing osmotic tablets have been described and manufactured which have had an osmotically active drug core which expands when contacted with gastric fluids and extrudes out a separate layer that contains an active drug. The core is divided into two layers one of which contains the active drug and the other contains a push layer of pharmacologically inactive ingredients which are osmotically active in the presence of gastrointestinal fluids. These tablets are provided with an aperture that is formed by punching or drilling a hole in the surface using a mechanical or laser drilling apparatus. A product of this type is disclosed in U.S. Pat. No. 4,783,337 and is sold commercially as Procardia XL.RTM..
The osmotic dosage forms that are disclosed in U.S. Pat. No. 4,783,337 are described as having a passageway which includes an aperture, orifice, hole, porous element, hollow fiber, capillary tube, microporous insert, pore, microporous overlay or bore which extends through the semipermeable lamina, the microporous lamina, or through the laminated wall. The patent also states that the passageway may be formed by mechanical drilling, laser drilling, eroding an erodible element, extracting, dissolving, bursting or leaching a passageway-former from the wall of the osmotic dosage form (col. 14, line 35 et seq.) which are implicitly pre-formed in the tablet during the manufacturing process. The only exemplified technique of forming a passageway in U.S. Pat. No. 4,783,337 is the use of a laser to drill a hole in the outer layer of the tablet.
U.S. Pat. No. 4,285,987 described an osmotic tablet which had a laser drilled aperture into the core of the tablet. The laser drilled hole was plugged with leachable sorbitol which was leached out in the presence of gastrointestinal fluid.
The present invention is concerned with providing an osmotic tablet having an aperture but does not have a separate "push" layer in the core which contains no medicament. In addition, a coating process has been invented which applies an insoluble coating to a tablet having an aperture without causing the aperture to become coated or clogged by the coating.